Coral
Anthozoa
Quick answer
Corals are small marine animals in the class Anthozoa, related to sea anemones and jellyfish, that often live in vast colonies of individual polyps. Reef-building corals secrete hard calcium carbonate skeletons that, over thousands of years, form the largest living structures on Earth. Many depend on algae living in their tissue for food and color, and a single colony can live for decades or longer.
Coral facts at a glance
| Scientific name | Anthozoa (class) |
|---|---|
| Diet | Filter feeder plus algae symbionts |
| Habitat | Warm, shallow tropical seas worldwide |
| Lifespan | Colonies can live decades to centuries |
| Size | Polyps mm-wide; colonies and reefs vast |
| Top speed | None; corals are fixed in place |
| Conservation status | Varies by species |
| Kingdom | Animalia |
|---|---|
| Phylum | Cnidaria |
| Class | Anthozoa |
Where it lives
Warm, shallow tropical seas worldwide, with the greatest diversity in the Indo-Pacific.
Tiny animals, giant reefs
Each coral is built from many small animals called polyps, soft cup-shaped bodies ringed with stinging tentacles. Reef-building corals secrete hard skeletons of calcium carbonate beneath them, and as generations stack up over thousands of years they form reefs. The Great Barrier Reef, made by countless coral colonies, is so large it can be seen from space.
A partnership with algae
Many corals host tiny algae called zooxanthellae inside their tissue, which photosynthesize and supply much of the coral's food and its bright color. In return the coral gives the algae shelter and nutrients, a partnership that lets reefs thrive in clear, sunlit, nutrient-poor tropical waters. Corals also catch plankton and tiny animals using their stinging tentacles, especially at night.
Reproduction and growth
Corals can reproduce both by budding, where polyps clone themselves to expand a colony, and by spawning, releasing eggs and sperm into the water. On many reefs, mass spawning events see corals release their eggs and sperm together on the same few nights of the year. Growth is slow, with many corals adding only a few centimeters or less per year.
Bleaching and conservation
When water becomes too warm or polluted, corals expel their algae and turn white, an event called bleaching that can kill them if conditions do not improve. Climate change, ocean acidification, pollution, and destructive fishing all threaten reefs worldwide. Because reefs support a quarter of all marine species, their protection is a major global conservation priority, and the status of individual coral species varies widely.
Frequently asked questions about the Coral
Is coral a plant or an animal?
Coral is an animal, not a plant. Each coral is made of many tiny animals called polyps, related to sea anemones and jellyfish, though many corals also host algae in their tissue.
How do corals build reefs?
Reef-building corals secrete hard skeletons of calcium carbonate beneath their polyps. As generations of coral grow and stack up over thousands of years, these skeletons form massive reefs.
What is coral bleaching?
Coral bleaching happens when stressed corals, often from water that is too warm, expel the algae living in their tissue and turn white. If the stress continues, the coral can starve and die.
What do corals eat?
Corals get much of their food from algae living in their tissue, which photosynthesize and share sugars. They also catch plankton and tiny animals using their stinging tentacles, mostly at night.
Are coral reefs important?
Yes. Coral reefs support around a quarter of all marine species, protect coastlines from waves, and provide food and income for hundreds of millions of people, making their conservation a global priority.
How long do corals live?
Individual polyps are short-lived, but coral colonies can persist for decades to centuries, and some deep-sea and massive reef corals are estimated to be thousands of years old.
